Group call management

ABSTRACT

A method of managing a group call involving a number of mobile communications devices include a network node identifying a radio access node adjacent a first radio access node. The method also includes a serving node creating the Group Call Area on basis of the first and adjacent radio access nodes. The method also includes establishing a signalling channel within a cell corresponding to the adjacent radio access node. The signalling channel includes an identifier corresponding to the Group Call area. The radio access nodes, or base stations, that have established a data communications channel with the mobile communications device have traffic and signalling channels established therein and are marked as an active cell of the Group Call Area.

FIELD OF THE INVENTION

The present invention relates to mobile telecommunications networks andto the coordination of group calls involving mobile terminals operatingin such networks; embodiments of the invention are particularly, but notexclusively, suited to coordinating group calls when members of thegroup move between cells of the mobile network.

BACKGROUND OF THE INVENTION

Conventional mobile telecommunications networks, for example, digitalcellular telecommunication networks according to the GSM Standard(Global System for Mobile Communications) provide voice broadcastservices that permit a subscriber to initiate a group broadcast calldirected to a group of other subscribers. Such voice broadcast servicefor GSM systems is specified in GSM Standard 03.68 and a related GSMStandard, namely GSM 03.69.

Typically, a particular group is identified by a group ID. A commoncontrol channel (for example the notification channel NCH in GSM)broadcasts a notification message including the group ID and adescription of the channel being used for the group call in the network.Thus, users having the correct group ID stored in their mobileterminals, for example stored in the SIM (Subscriber Identity Module)card of a GSM mobile unit, can recognize the notification message, andcan then connect to the group call by tuning to the channel described inthe notification message. Furthermore in conventional Voice Group CallService (VGCS) systems a given user can request and obtain an uplinkchannel, thereby permitting the user to speak to the group. A givenmobile user must have a subscription with the group call serviceprovider in order to be permitted to initiate a group call orparticipate in a group call.

Group call attributes including, for example, a listing of the cells inwhich the group call is broadcasted (the Group Call Area) areconventionally compiled in a separate network node database, for examplethe Group Call Register (GCR) in GSM networks. The group call registeris typically associated with a Mobile Switching Centre (MSC) in GSMsystems.

A particular problem is encountered with group calls when multiple groupcalls, each having the same group ID, are conducted within overlappingcells. In one conventional arrangement, a mobile station wanting to joina group call will select whichever of the notification broadcastmessages that are broadcast on the notification channel in the cell isfirst received by the mobile device, so that selection of a group tojoin can be viewed as random. In relation to mobile devices that arealready engaged in a group call at the time of moving into anoverlapping cell, International patent application having publicationnumber WO0131964 describes a mechanism by which these groups will bemerged so as to form a single group call (with a larger number ofparticipants), whilst other known mechanisms constrain mobile devices toremain with the group to which they were associated prior to moving intothe cell. In all of these configurations, there is no means ofintelligently selecting between group calls: selection is eitherperformed randomly, or hard wired based on initial group designations,or not possible. In addition there is no means of restricting members ofa group call: provided a mobile user has a subscription with the groupcall service provider, its terminal can join a group call.

Another problem is encountered when mobile devices move between cells:subscribers of conventional group call services are typically allowed tomove from cell to cell while remaining in the group call, assuming thatthe group call is broadcast in each new cell into which the subscriberroams. However, if the group call is not being broadcasted in the newcell, then the group call will no longer be available to the subscriber.Further, changing cells often requires a short interruption of thesubscriber's reception of the group call until the subscriber's mobileterminal has listened to the notification channel in the new cell andtuned to the proper group call channel in the new cell.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there isprovided a method of setting up a call group for participation in agroup call by a plurality of mobile devices in a mobiletelecommunications network, the mobile telecommunications networkcomprising a serving node operable to transceive data to and from themobile telecommunications devices, the method comprising:

-   -   receiving, at a serving node, data indicative of a group        identifier from a said mobile terminal registered with the        mobile telecommunications network; and    -   defining a Group Call Area using the received group identifier,        the defined Group Call Area being accessible by the serving node        so as to enable the serving node to discriminate one call group        registered with said telecommunications network from another        call group registered with said telecommunications network.

Thus with embodiments of the invention Group Call Areas are defined onthe basis of an identifier that is unique to the group; this enables twoor more group calls having the same group calling identifier to exist inthe same cell without interfering with one another. Conveniently thetelecommunications network holds data identifying group call numbers,and at least one of the group call numbers is reserved for dynamic groupcalls. As a result the group call number can be used to identify thegroup call as a static type of group call or a dynamic type of groupcall, and the processes performed by the network selected accordingly.

According to a further aspect of the present invention there is provideda method of managing a group call involving a plurality of mobilecommunications devices, said plurality of mobile communications devicesbeing registered with a telecommunications network via a serving node,the serving node being operable to transceive data to and from aplurality of radio access nodes so as to communicate with saidregistered mobile communications devices, in which at least a first ofsaid radio access nodes has established a data communications channelwith a mobile communications device of the plurality for conducting thegroup call, the method comprising:

identifying a radio access node adjacent the first radio access node;

defining the Group Call Area on basis of the first and adjacent radioaccess nodes; and

establishing a signalling channel within a cell corresponding to saidadjacent radio access node, said signalling channel having an identifiercorresponding to the Group Call Area.

The telecommunications network comprises a plurality of radio accessnodes in the form of base stations; the serving node—or switch—isoperable to transceive data to and from the base stations as perconventional network arrangements. Whichever base station hasestablished a data communications channel with the mobile communicationsdevice has traffic and signalling channels established therein and ismarked as an active cell of the Group Call Area;

In addition, base stations adjacent the active base station are added tothe Group Call Area, signalling channels are established in theseadjacent cells, and each signalling channel has an identifiercorresponding to the Group Call Area. This method of channel allocationand deallocation provides a solution to the problem in the prior art inwhich channels have to be created as a mobile station moves into a newcell; by contrast, and because a signalling channel in any potential“next” cell has already been established, it is relativelystraightforward to allocate a traffic channel therein.

Conveniently traffic channels can be created in response to a signallingrequest message from the mobile communications device identifying theadjacent radio access node: this indicates that the mobile device hasmoved into one of the previously designated adjacent cells and thuseffectively changes the “active” cell to that which received thesignalling request message from the mobile device. As the active cellchanges, so do the base stations that can be considered adjacent to the“active” cell, and thus the actual Group Call Area. The Group Call Areacan be updated by the network in response to traffic deallocationmessages sent from a base station in the event that the base station isno longer transceiving data with a mobile device associated with thegroup call. These deallocation messages can additionally be used todelete cells from the Group Call Area that were adjacent to a cellpreviously designated the active cell. As a result, in preferredarrangements the Group Call Area includes cells immediately surroundingcurrently active cells.

According to a further aspect of the present invention there is provideda group call management system for managing a group call involving aplurality of mobile communications devices, said plurality of mobilecommunications devices being registered with a telecommunicationsnetwork via a serving node, the serving node being operable totransceive data to and from a plurality of radio access nodes so as tocommunicate with said registered mobile communications devices, in whichat least a first of said radio access nodes has established a datacommunications channel with a mobile communications device of theplurality for conducting the group call. The group call managementsystem comprises:

a network node arranged to identify a radio access node adjacent thefirst radio access node in response to a service request messageidentifying the first radio access node; and

means for configuring the Group Call Area on basis of the first andadjacent radio access nodes,

wherein at least some said adjacent radio access nodes are arranged toestablish a signalling channel, said signalling channel having anidentifier corresponding to the Group Call Area.

In one arrangement the serving node comprises the means for configuringthe Group Call Area and the group call management system is collectivelyconfigured to provide the functionality described above.

It can therefore be seen that embodiments of the invention provide ameans of intelligently controlling parties joining a group call andselectively coordinating signalling between cells so as to avoidinterruptions to reception of the group call.

Further features and advantages of the invention will become apparentfrom the following description of preferred embodiments of theinvention, given by way of example only, which is made with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing various components of astandard configuration of a mobile network;

FIG. 2 is a timing diagram showing communication between various of thecomponents shown in FIG. 1 when registering a mobile station for a groupcall according to an embodiment of the invention;

FIG. 3 is a schematic block diagram showing a plurality of cells shownin FIG. 1;

FIG. 4 is a timing diagram showing communication between various of thecomponents shown in FIG. 1 when setting up a group call according to anembodiment of the invention;

FIG. 5 is a timing diagram showing communication between various of thecomponents shown in FIG. 1 in relation to movement of a member of thegroup call into a new cell according to an embodiment of the invention;

FIG. 6 is a timing diagram showing communication between various of thecomponents shown in FIG. 1 in relation to movement of a member of thegroup call from an old cell according to an embodiment of the invention;and

FIG. 7 is a timing diagram showing communication between various of thecomponents shown in FIG. 1 when coordinating termination of a groupcall.

DETAILED DESCRIPTION OF THE INVENTION

As described above, embodiments of the invention are concerned withcoordinating movement of group calls through a cellular network, inparticular with intelligently controlling parties joining a group calland selectively coordinating signalling between cells so as to avoidinterruptions to reception of the group call as it moves. In order toappreciate the level at which embodiments of the invention operate, anoverview of a Public Land Mobile Network (PLMN) 1, within which suchembodiments can operate, will first be described with reference to FIG.1.

The PLMN network shown in FIG. 1 comprises a cellular network such as aGSM or UMTS network (only one cell 100 being shown in FIG. 1). The cell100 has a limited coverage and is served by the PLMN 1 via a BaseTransceiver Station (BTS) 102 and a Base Station Controller (BSC) 103,which form a Base Station System (BSS) 105. The BSC 103 is connected toa Mobile Switching Center (MSC) 107 which is an exchange and is arrangedto perform all switching functions for mobile stations such as MS 101located in a geographical area designated as the MSC area. As shown inFIG. 1, the MSC 107 is connected to a Service Control Point SCP 117 thatis arranged, on the basis of the network subscription associated with MS101, to provide MS 101 with access to various intelligent networkservices, in this case, a group call service.

In operation, the MSC 107 takes into account the impact of theallocation of radio resources and the mobile nature of the subscribers,and performs procedures required for location registration, hand-overof, and call set-up for, served mobile stations. The MSC 107 isconnected to a Home Location Register (HLR) 115, which is a databasearranged to manage subscription data relating to mobile subscribers suchas MS 101. The PLMN I may include one or several HLRs 115, depending onthe number of mobile subscribers, the capacity of the equipment and theorganization of the PLMN network 1. The HLR 115 is arranged to storedata identifying the location of mobile subscribers managed by each HLR115 (e.g. in order to be able to route calls thereto); identificationnumbers attached to each mobile subscription (e.g. International MobileSubscriber identity (IMSI); Mobile Subscriber ISDN Number (MSISDN));communication service subscription information, service restrictions(e.g. roaming limitations); general subscriber attributes andpreferences; and supplementary service information including parametersassociated with these services. In terms of communication between thevarious components of the PLMN 1, the MSC 107, HLR 115 and SCP 177 maysend and receive data via a variety of signaling protocols, includingbut not limited to, Signaling System Number (SS#7) Mobile ApplicationPart (MAP).

Additionally, the MSC 107 is connected to a Visitor Location Register(VLR) 113, which is arranged, as in known configurations, to receivedata from mobile subscribers MS 101 in this MSC area and pass thisinformation onto the HLR 115; additionally the VLR 113 is arranged toreceive data from the HLR 115 indicating sets of services and triggersavailable to MS 101. One of the sets of services available to the MS 101in an embodiment of the invention is group calls to group ID 888, itbeing assumed that the subscriber corresponding to MS 101 has subscribedto a group call service that is coordinated by the SCP 117. As a result,call setup requests from the MS 101 that contain group ID 888 have theeffect of triggering the MSC 107 to send signalling messages to the SCP117. In addition, the SCP 117 and MSC 107 are configured with bespokefunctionality so as to configure Group Call Areas according to anembodiment of the invention. This will now be described with referenceto FIGS. 2-6 for the particular example of a group call beingcoordinated in relation to train employees travelling on a train fromLondon to Edinburgh.

Starting with FIG. 2, the steps involved in registration of the mobilestation 101 with the group call service will be described. At step S201,the mobile station 101 sends a Registration request message, whichincludes a unique identifier for the group, TFN. In the current examplethe unique identifier conveniently includes an identity of the train,this having previously been provided to the mobile station 101 (andindeed to other mobile stations corresponding to the personnel on thetrain). The registration request is forwarded to the MSC 107 via the BSS105, and this triggers a registration request message to be forwarded tothe SCP 117 at step S203. As can be seen from FIG. 2, the registrationrequest message received by the SCP 117 comprises the group identifierTFN and the MSISDN of the individual mobile station 101 from which theregistration request originated at step 5201. In the current example theunique identifier TFN identifies a functional number of the particulartrain, and can be composed by the following parts: call type (trainnumber), train running number and function code (e.g. driver). Thus forexample assuming a train to have a train number of 2, a train runningnumber of 00175 and function code of 01, the identifier TFN received bythe SCP 117 can be 2 00175-01. It will be appreciated that theidentifier can be made up of data identifying other characteristics ofthe train.

In response to receipt of the MSISDN and TFN information, the SCP 117firstly checks that this requesting mobile station 101 is authorised toparticipate in a group service and, if so, updates its mappings betweenmobile stations and group identities (step S205). These data can then beused in handling subsequent requests for group calls. Assumingregistration to be successful, the SCP 117 transmits an acknowledgmentmessage at step S207 to the MSC 107, which sends this back to the mobilestation 101 via the BSS 105. Whilst registration in respect of only onemobile station is shown in FIG. 3, it will be appreciated that forarrangements in which registration is a prerequisite to participation ina group call, all such mobile stations will be required to register withthe service. It is, however, to be noted that the particularregistration process described herein is exemplary only and entirelyindependent of the processes involved in setting up and managing groupcalls according to embodiments of the invention. Indeed registrationwith a group call service can be effected via Over The Air (OTA) SIMupdates in one alternative arrangement, whilst embodiments of theinvention do not necessarily require all participating mobile devices tohave preregistered with a group service (e.g. in the event that thegroup call is of an open VGCS type).

Turning now to FIG. 3, in the current example it is assumed that thetrain is in the process of moving through cells 100 a, 100 b, 100 c, andthat a group call request is received from the mobile station 101 whenit is located in cell 100 a. With reference also to FIG. 4, a group callrequest is received by the mobile station 101 transmitting a standardgroup call setup message (step S401), the message comprising the uniqueidentifier for this call (TFN), together with the group ID for the call(in this example 888). This is received by the SCP 117, together withthe Cell ID (in this case 100 a corresponding to base station BS 105 a).At step S407 the SCP 117 performs a look-up of the database holding dataindicating ongoing group calls having this group ID (888) and a uniquegroup identity matching that received at step S401. In the currentexample the SCP 117 is configured to match the train running numberportion of the Train Functional Number (TFN), but it will be appreciatedthat the entire string of the TFN could alternatively be used, or indeeda different part or transformation thereof. In this case no such groupcall exists, so at step S407 an entry is created in the group call tablemanaged by the SCP 117 for a new call having group identity TFN andgroup ID 888.

In embodiments of the invention the SCP 117 additionally stores, or hasaccess to, a table listing static group call numbers and dynamic groupcall numbers. For illustrative purposes it is assumed that group IDswithin the range 880-888 have been reserved for dynamic group calls,and, if a group call is determined to correspond to a dynamic groupcall, the functionality invoked of the SCP 117 is different to thatwhich is invoked according to conventional methods for handling dynamicgroup calls. It is to be noted that static group calls are handledaccording to conventional methods and are outside of the scope of thepresent invention.

In the current example the group ID is 888, which indicates a dynamicgroup call. In response to identifying the group call to be of thedynamic type the SCP 117 identifies all cells that are adjacent to thecurrent cell 100 a, e.g. by means of a prestored cell configuration map.A message comprising the list of neighbouring cells is subsequently sentto the MSC 107 at step S409, together with the unique group identifierTFN. This message comprises an instruction for the MSC 107 to create aGroup Call Area based on these neighbouring and originating cells (stepS411). Referring back to FIG. 3, in the current example the cellsneighbouring the cell of origin 100 a are cells 100 x and 100 b;accordingly step S411 involves the MSC 107 updating a group callregister database held locally by the MSC 107 so as to include thisnewly created dynamic Group Call Area with cells 100 x, 100 a, 100 b.

At step S413 a call connection message is sent to the mobile station 101so as to start the dynamic group call. In addition a notificationmessage comprising the dynamic group ID 888 is broadcast to all mobilestations within the Group Call Area, which in this example comprisescells 100 x, 100 a and 100 b (step S417), the BSS 105 a, 105 b havingpreviously been instructed to set up signalling and traffic channels inresponse to the notification received at step S415. This message isbroadcast on the Notification channel NCH and enables all other mobilestations having the unique group identifier TFN and subscribing to groupcall 888 to join the call in the call group area 100 x, 100 a, 100 b,and thereby make use of the traffic channels established therein.

The steps relating to the processes performed in respect of cells 100 xand 100 b—i.e. those adjacent to the cell 100 a in which the group calloriginated—will now be described in relation to cell 100 b. Havingestablished the traffic channel in cell 100 b, base station BSS 105 bsends a standard TCH allocation message to the SCP 117 via the MSC 107(step S418), causing the SCP 117 to store an entry in its database forthis neighbouring cell 100 b (step S419). Meanwhile, and in accordancewith standard methods, the BSS 105 b monitors for a reply on the uplinktraffic channel from a mobile station within cell 100 b for apredetermined time period (step S421). In the event that there is noresponse within this period, the BSS 105 b transmits a deallocationtraffic channel notification message to the SCP 117 via the MSC 107(step S423), causing the SCP 117 to update its entry for traffic channelin cell 100 b as deallocated. It is to be noted that whilst the trafficchannel is removed, the signalling channel is not pulled down;furthermore the deallocation of the traffic channel has no bearing onthe Group Call Area—this remaining as 100 x, 100 a, 100 b.

Group Call Areas created according to embodiments of the invention cantherefore be characterised as comprising active cells and passive cells.The active cells are those for which signalling and traffic channelsexist, and there are as many active cells as there are cells comprisingparticipants in the group call. The passive cells are those thatneighbour the active cells and in respect of which only signallingchannels exist. Thus in the current example, for the time in which thetrain and all personnel thereon are located within cell 100 a, there isone active cell (100 a) and two passive cells (100 x, 100 b). Thismethod of channel allocation and deallocation provides a solution to theproblem in the prior art in which channels have to be created as amobile station moves into a new cell, because a signalling channel inany potential “next” cell has already been established, making itrelatively straightforward to allocate a traffic channel therein, aswill now be described with reference to FIG. 5.

Referring back briefly to FIG. 3, as the train moves along trajectoryT1, it enters cell 100 b after a certain period of time. As a result ofthe notification messages transmitted at step S415, cell 100 b alreadyhas a notification channel associated with this group call (ID 888 and aGroup Call Area having identifier 00175). Accordingly the mobile station101 will detect the existence of the group call having ID 888 via thenotification channel as soon as it enters cell 100 b; in response themobile station 101 checks the group ID (888) and the identifier of theGroup Call Area (00175) against unique identifiers registered with themobile station 101. Since, in this case, the mobile station 101 hasregistered for Group Call Area having identifier 00175, the group callcan be conducted in this cell 100 b; as a result mobile station 101subsequently sends a notification response message to the BSS 105 b(step S501), the notification response message comprising the Group CallArea (00175) and group ID (888). When received by the BSS 105 b, the BSS105 b allocates a traffic channel therein (step S502) and sendsnotification of the traffic channel allocation to the SCP (step S503)for cell 100 b.

Upon receipt of the traffic channel allocation message the SCP 117identifies all cells that are adjacent to the current cell 100 b, againby referring to the prestored cell configuration map as described abovein relation to step S407, and updates the status for cell ID 100 b ashaving an active traffic channel therein (step S505). Thereafter,identifiers of cells adjacent to the current cell 100 b are sent to theMSC 107, which in this case is cell 100 c, with an instruction to theMSC 107 to update the Group Call Area to include this cell 100 c (stepS507). Upon receipt of this instruction message the MSC 107 updates itstable (step S508) and sends a notification message to cell 100 c newlyadded to the Group Call Area (step S509); this causes the BSS 105 c totransmit a notification message to all mobile stations in the cell 100 c(step S511) and the process then proceeds as described from step S415 inFIG. 4.

In addition to adding cells to the Group Call Area as the group callmoves, cells that were previously part of the Group Call Area aredeleted therefrom. Referring to FIG. 6, deletion of cells from the CallGroup Area is conveniently performed on the basis of standard signallingmessages, namely a traffic deallocation message. This message will betransmitted by BSS 105 a when the train (and thus mobile station 101)has moved out of cell 100 a, because once the train has moved into cell100 b there are no mobile stations in cell 100 a that can respond to thenotification messages having Group Call Area (00175) and group ID (888).Once the traffic deallocation message has been received by the SCP 117,the entry corresponding to cell ID 100 a is updated with the status ofthe traffic channel. In addition the SCP 117 searches for cells listedin the Group Call Area that have deallocated status and that are notadjacent the currently active cell(s) (i.e. cell(s) for which thetraffic channel is active). Referring back to FIG. 3, in the presentexample the currently active cell is 100 b, and there are threeunactive, or passive, cells 100 x, 100 a, 100 c. Since cell 100 x is nota neighbour of the currently active cell 100 b, it is removed from theCall Group Area (step 603) by the SCP 117. A message is then sent to theMSC 107, instructing the MSC 107 to delete cell 100 x from the GroupCall Area that it stored at step 411; this deletion is effected at stepS607 and the MSC 107 then proceeds to instruct the BSS 105xcorresponding to the deleted cell to stop sending notification messagesvia the signalling channel NCH (step S607).

As described above, there will be as many active cells as there areparticipants of the group call that occupy different cells; thus whilstin the example shown in FIG. 3 it is assumed that all participants ofthe group call are present in a single cell at any one time, for caseswhere the train is long and/or participants are distributed along thelength of the train, it can expected that there will be several activecells and a commensurately greater number of passive cells than thoseshown in FIG. 3.

It will be appreciated that the steps shown in FIGS. 5 and 6 will berepeated in respect of each cell that the group call enters so as toensure that the activation of traffic channels in any given active cellis synchronised with the activation and deactivation of signallingchannels in prospective, current and previous passive cells. In summary,and by way of generalising the ongoing group call management process,allocations and deallocations of voice channels are reported to the MSC107 by the BSS 105 a . . . 105 c. Voice channel allocations are used bythe MSC 107 to request the service node 117 to find the adjacent cellsof the active cell (i.e. the cell in which the voice channel is active).These cells are then added to the Group Call Area. Deallocationinformation is used to remove all cells from the Group Call Area in casethey are no longer neighbour cells of a cell in which a voice channel iscurrently allocated.

When a group call is terminated, various messages are passed between thevarious mobile and network entities, as will now be described withreference to FIG. 7. Typically the group call will be terminated by themobile station 101, by means of a standard termination request message(step S701). For illustration purposes it will be assumed that thetermination request is received when the mobile station is in cell 100b, so that this message is received from the mobile station 101 by BSS105 b. The BSS 105 b relays the termination request message to the MSC107, which creates a group call termination instruction identifying theGroup Call Area (00175) and group ID (888) and transmits this message tothe SCP 117. In response the SCP 117 removes all cells from the mappingcorresponding to this Group Call Area and Group ID (step S705); inaddition, the SCP 117 sends an instruction to the MSC 107, instructingthe MSC 107 to delete the cells from the Group Call Area associated withthis group call (step S707). When received, the MSC 107 identifies thegroup call that it created at step 411 and sends termination messages toall BSS 105 a, 105 b, 105 c currently listed against that Group CallArea (step S709) so as to effect termination of any traffic andsignalling channels.

From the foregoing it can be seen that in addition to conventionalfunctionality specified in GSM Standard 03.68, the SCP 117 is configuredwith a means for transmitting an instruction to the MSC 107 to define aGroup Call Area including a plurality of neighbouring cells (e.g. stepS409), and to send instructions to add and delete cells to and from theGroup Call Area (e.g. S507, S605). The SCP 117 is additionallyconfigured to receive traffic allocation and deallocation messages inrelation to the neighbouring cells, these traffic channel messagestriggering updates to the register holding details of group calls (S407,S505, S603) and causing the SCP 117 to send the afore-mentioned messagesto the MSC 107.

The MSC 107 is similarly equipped with bespoke functionality in the formof means for updating a repository holding details of group calls andcells relating thereto in the event that a group call is determined tobe of the dynamic type (i.e. having a number between 880-888 in thecurrent example); the MSC 107 can add to, and delete from, the cellsbelonging to a Group Call Area upon instruction from the SCP 117 asshown e.g. at step S411, 508, 607. In addition, the MSC 107 isconfigured to transmit traffic allocation and deallocation instructionmessages to the SCP 107 (these being received from the BSS using astandard uplink reply/notification feature). This additionalfunctionality can be implemented as software running on, and storageaccessible to, the switch 107 and SCP 117.

In addition the mobile stations are equipped with means to discriminatebetween dynamic group calls (i.e. group calls having Ids between880-888) on the basis of Group Call Area (i.e. group identifiers thatare unique for the group—in the foregoing example this is the trainidentity). This functionality can either be implemented on the mobilephone or on the removable module (SIM) associated with the subscriptionof the user. Such functionality is similar to the filtering of ShuntingGroups in the GSM-Railway (GSM-R) environment. This therefore enablesany given mobile station to participate in two dynamic group callshaving the same group ID (e.g. 888) provided the mobile station haspreviously registered for each of the groups (i.e. in respect of eachunique identifier).

It will be appreciated from the foregoing that by using an identifier todefine the Group Call Area embodiments of the invention enable groupshaving the same group number to co-exist distinct from one anotherwithin the same group of cells. This is an improvement of the prior art,in which there is either no means of distinguishing one Group Call Areafrom another Group Call Area if their physical locations overlap (withthe result that the groups are joined into a single group), or thejoining of a group is controlled by which notification channel a mobilestation communicates with first (with the result that selection of agroup by the mobile station is essentially a random process).

Additional Details and Modifications

Whilst in the foregoing embodiment the use of a unique group identifieris described in the context of dynamic group calls, this aspect of theinvention could also be utilised in respect of static group calls, sinceit provides a means of discriminating between different group callsexisting in a given area. Thus while the foregoing embodiment relates tothe coordination of group calls in the context of train travel,embodiments of the invention could alternatively be employed inenvironments that involve mobile and static group calls. Examplesinclude groups of workers in a factory, emergency services (inparticular sections of the police force or fire brigade), teamsparticipating in sporting events such as sailing, groups ofarchaeologists distributed over a given area, or groups of constructionworkers distributed over a construction site etc.

The above embodiments are to be understood as illustrative examples ofthe invention. Other embodiments are envisaged, for example in relationto group calls involving more than one MSC. In such a scenario one MSCis designated as controller of the group call: the Anchor MSC. If theGroup Call Area includes cells which are not under the control of theAnchor-MSC, the MSC for those cells also participate in the group callas a Relay MSC. This enables movement of the group call as and when adifferent MSC becomes available.

It is to be understood that any feature described in relation to any oneembodiment may be used alone, or in combination with other featuresdescribed, and may also be used in combination with one or more featuresof any other of the embodiments, or any combination of any other of theembodiments. Furthermore, equivalents and modifications not describedabove may also be employed without departing from the scope of theinvention, which is defined in the accompanying claims.

1. A method of managing a group call involving a plurality of mobilecommunications devices, said plurality of mobile communications devicesbeing registered with a telecommunications network via a serving node,the serving node being operable to transceive data to and from aplurality of radio access nodes so as to communicate with saidregistered mobile communications devices, in which at least a first ofsaid radio access nodes has established a data communications channelwith a mobile communications device of the plurality for conducting thegroup call, the method comprising: identifying a radio access nodeadjacent to the first radio access node; the serving node receiving aservice response message from a network node, said service responsemessage comprising data identifying a Group Call Area; the serving nodedefining the Group Call Area based upon the first radio access node andthe adjacent radio access node; the serving node transmitting signallinginstruction messages to said radio access nodes defined by the GroupCall Area, said signalling instruction messages comprising instructionsto establish a signalling channel; establishing the signalling channel,prior to establishing a traffic channel, within a cell corresponding tosaid adjacent radio access node, said signalling channel having anidentifier corresponding to the Group Call Area; broadcasting anotification message for the group call within the Group Call Area usingat least said signalling channel; receiving a notification responsemessage having the identifier corresponding to the Group Call Area froma mobile communication device; and establishing the traffic channel foruse in the group call within the cell corresponding to said adjacentradio access node.
 2. A method according to claim 1, further comprisingcreating a data communications channel in response to a signallingrequest message from the mobile communications device identifying theadjacent radio access node, whereby to define said adjacent radio accessnode as the or a further first radio access node.
 3. A method accordingto claim 2 including identifying a plurality of radio access nodesadjacent the first radio access node, the Group Call Area being definedon the basis of said first and plurality of adjacent radio access nodes.4. A method according to claim 3 including identifying a radio accessnode in the Group Call Area not adjacent to said first radio accessnode, and removing the radio access node so identified from the GroupCall Area.
 5. A method according to claim 1, including identifying saidradio access node adjacent the first radio access node on the basis of apre-stored cell configuration map.
 6. A method according to claim 5, inwhich said identifying of said radio access node adjacent the firstradio access node is performed at a Service Control Point.
 7. A groupcall management system for managing a group call involving a pluralityof mobile communications devices, said plurality of mobilecommunications devices being registered with a telecommunicationsnetwork via a serving node, the serving node being operable totransceive data to and from a plurality of radio access nodes so as tocommunicate with said registered mobile communications devices, in whichat least a first of said radio access nodes has established a datacommunications channel with a mobile communications device of theplurality for conducting the group call, the group call managementsystem comprising: a network node configured to identify one or moreradio access nodes adjacent to the first radio access node in responseto a service request message identifying the first radio access node;wherein the serving node is configured to receive a service responsemessage from the network node, said service response message comprisingdata identifying a Group Call Area; wherein the serving node is furtherconfigured to create the Group Call Area based upon the first andadjacent radio access nodes; wherein the serving node is furtherconfigured to transmit signalling instruction messages to said radioaccess nodes defined by the Group Call Area, said signalling instructionmessages comprising instructions to establish the signalling channels;and wherein at least some of said adjacent radio access nodes areconfigured to: establish a signalling channel prior to establishing atraffic channel, said signalling channel having an identifiercorresponding to the Group Call Area, broadcast a notification messagefor the group call within the Group Call Area using at least saidsignalling channel, receive a notification response message having theidentifier corresponding to the Group Call Area from a mobilecommunication device, and establish a traffic channel for use in thegroup call within the cell corresponding to said adjacent radio accessnode.
 8. A group call management system according to claim 7, whereineach said adjacent radio access node is arranged to create a datacommunications channel in response to a signalling request message fromthe mobile communications device identifying the adjacent radio accessnode, whereby to define said adjacent radio access node as the or afurther first radio access node.
 9. A group call management systemaccording to claim 8, wherein the network node is arranged to identify aplurality of radio access nodes adjacent the first radio access node,the Group Call Area being defined on the basis of said first andplurality of adjacent radio access nodes.
 10. A group call managementsystem according to claim 7 wherein the network node is arranged toidentify a radio access node in the Group Call Area not adjacent to saidfirst radio access node, and remove the radio access node so identifiedfrom the Group Call Area.
 11. A group call management system accordingto claim 7, including identifying said radio access node adjacent thefirst radio access node on the basis of a pre-stored cell configurationmap.
 12. A group call management system according to claim 11, in whichsaid identifying of said radio access node adjacent the first radioaccess node is performed at a Service Control Point.